A three-dimensional photonic band gapstructure based on self-assembled crystals of polystyrene microspheres was fabricated by filling the pores with metallic silver. An almost complete stop band at 580–600 nm is observed in the optical transmission spectra. In comparison with pure polystyrene colloid crystals, the absorption band of Bragg diffraction in the composite was much more intense and broader, due to an enlargement of the contrast between the spheres and the background. A shift to shorter wavelengths in the band occurred because of a decrease in the average refractive index.

The pulsed operation of a GaAs/AlGaAs quantum-cascade laser is reported up to 258 K. These devices emit at 11.3 μm and are based on a plasmon-confinement waveguide. To optimize the material gain, the active region is designed to diminish electron escape to continuum states. Gain and threshold measurement show evidence of better carrier confinement and improved thermal behavior compared to GaAs quantum-cascade lasers. The maximum peak-collected power at 77 K is 520 mW per facet and still 27 mW at 258 K. The temperature dependence of the threshold current density is characterized by a

We report room-temperature injection lasing of self-assembled InP/GaInP quantum dots.Stimulated emission occurs via the ground state at for cavities as short as 0.5 mm. Threshold current densities of 2.3 kA/cm2 and external differential quantum efficiencies of 8.5% have been measured for 2 mm long devices. Light output power as high as 250 mW without saturation effects can be reached in pulsed excitation. Analysis of temperature-dependent laser emission indicates the thermal coupling of charge carriers in different quantum dots at higher temperatures.

An experimental analysis of the distribution and thickness of the bulk nonlinearity induced in poled silica is reported. The second-order susceptibility decreases exponentially from the anodic interface. Maker fringe patterns showing a double structure are interpreted in relation to the presence of two nonlinear profiles, one concentrated near the anodic surface and another extending into the bulk of the sample. The Maker fringe theory is properly generalized and a double fitting technique reproducing well the experimental results is used to characterize the induced nonlinearities. The dependence of the second-harmonic signal on the poling temperature is given, which is different from that of sol-gel silica.

This letter reports on the high characteristic temperature of InGaAs/GaAs quantum-dot lasers at room temperature. Self-assembledquantum dots were grown using low-growth-rate molecularbeam epitaxy, and continuous-wave lasing occurred at the dot ground level of 1.26 μm at 25 °C. The characteristic temperature of the threshold currents was 120 K, and ground-level lasing was observed up to 100 °C. Comparing the lasing performances and the spontaneous emissionspectra with those of 1.3 μm emission dots, we found that the large volume density, deep potential, and high quantum efficiency were key points for improving the temperature characteristics.

Joule heating is one of the dominant mechanisms determining the transverse mode formation in vertical-cavity surface-emitting lasers at high injection currents. We give experimental evidence that in this operation regime, strong heating results in local gain suppression in the center of the laser, which overbalances the confining effect of thermal lensing, and thus favors the formation of high order modes. From our investigations of small aperture devices, we conclude that efficient heat removal is crucial for achieving single mode emission at high injection currents.

Far-infrared spontaneous emission at 300 K and lower temperatures, due to intersubband transitions in self-organizedquantum dots, has been characterized. Measurements were made with a multidot layer near-infrared (∼1 μm) interband laser. The far-infrared signal, centered at 12 μm, was enhanced after the interband transition reached threshold at 300 K. The results are explained in terms of the carrier dynamics in the dots.

Energy transfer between two laser beams writing a volume hologram in a photorefractive polymer composite is applied to video-rate optical processing applications. A net increase in image intensity as high as a factor of 37 can be observed within one video frame time (33 ms) using a total beam intensity of and applied electric field. Moving object detection (novelty filtering) is also demonstrated.

We report on the realization of a quantum cascade laser based on strained grown on GaAs substrate using molecular beam epitaxy. Lasing at 10.40 μm and at 9.45 μm was achieved with a good temperature performance showing a between 125 and 200 K and a maximum working temperature exceeding Between 78 and 130 K a considerably higher of 291 K is found. The decreasing with higher temperatures is due to misalignment of the injector with the upper laser level at elevated temperatures, thermal activation of tunneling of carriers above 130 K, and increasing carrier leakage from the injector into the continuum.

Experimental measurements of the injection lock band of an angled-grating distributed feedback laser have been performed systematically as a function of the unlocked slave laser power. Fringe visibility measurements were used to ascertain the quality of the lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental data show increasing spectral instabilities under optical injection as the slave laser power is increased, resulting in the stable portion of the lock band decreasing in width.

The spatiotemporal evolution of a 10-femtosecond light pulse (λ=805 nm) propagating through uncoated and metal-coated near-field fiber probes is analyzed theoretically within a two-dimensional model for and polarization of the incident field. Internal reflection inside uncoated fiber probes (cone angle of 28°) results in an efficient guiding towards the fiber tip and a diffraction-limitedspatial resolution of about 260 nm≈λ/3 in case of polarization. While the transmission through uncoated fiber probes has negligible effects on the temporal and spectral pulse profile, strong modifications are observed for metal-coated aperture probes. The wavelength-dependent aperture transmission gives rise to a pronounced blueshift and spectral narrowing of the transmitted pulses.

A theoretical model has been developed to simulate plasma formation and evolution during the early stage of picosecond laser ablation of solids. Surface electron emission was implemented as one boundary condition for plasma development above the target. The simulation results indicate that a plasma forms, with electron density on the order of during the picosecond laser pulse. Laser induced gas breakdown assisted by electron emission from the target was found to be the origin of the plasma. In agreement with experimental measurements, longitudinal movement of the electrons inside the plasma was suppressed after the laser pulse. The suppression of the plasma can be attributed to the development of a strong electric field above the target.

Siliconcarbide and carbonnanostructures were produced by pyrolysis of organosilane or aromatic compounds in nanoporous sol-gelsilicaglasses. Intense photoluminescence was observed in the visible and the near infrared regions, depending on material processing. Emission bands at 2.97, 2.67, 2.53, 2.41, 2.24, 2.09, 1.93, 1.13, 1.00, and 0.85 eV were observed in samples prepared at temperatures between 870 and 1220 K. Phosphorescence emission showed two lifetime components at 300 K: a 0.03 s component and a very long component of 0.5–4 s that depends on the precursors and sample processing. These lifetimes approximately doubled at 77 K. The visible emission increased significantly as the temperature was elevated from 77 to 950 K, suggesting thermally assisted light emission from sites in the silicaglasses containing SiC/C nanostructures. Surface SiCvacancy defects modeled using integrated ab initio quantum mechanics/molecular mechanics calculations suggest phosphorescence may originate from C vacancy (Si–Si dimers) in the visible and Si vacancy in the near infrared.

We report the observation of visible cathodoluminescence(CL) of Tb ions implanted into amorphous AlN films produced by sputtering. The implanted samples were subjected to thermal annealing treatment up to 1100 °C to optically activate the incorporated ions. The results show that up to 1000 °C annealing temperature the films remain amorphous and the emission intensity increases. The amorphous AlN:Tb films were characterized by x-ray diffraction,CL, and CL kinetics measurements. The sharp characteristic emission lines corresponding to intra--shell transitions are resolved in the spectral range from 350 to 750 nm, and observed over the temperature range from 7 to 330 K due to the transitions from and levels toward the to 6) multiplets. Finally, CL kinetics measurements have revealed that decay times of and transitions are in the range 0.94–0.77 and 0.49–1.61 ms at 300 K, respectively.

It has been shown recently that Au labeling [V. C. Venezia, D. J. Eaglesham, T. E. Haynes, A. Agarwal, D. C. Jacobson, H.-J. Gossmann, and F. H. Baumann, Appl. Phys. Lett. 73, 2980 (1998)] can be used to profile vacancy-type defects located near half the projected range in MeV-implanted Si. In this letter, we have determined the ratio of vacancies annihilated to Au atoms trapped (calibration factor “k”) for the Au-labeling technique. The calibration experiment consisted of three steps: (1) a implant into Si(100) followed by annealing at 815 °C to form stable excess vacancy defects; (2) controlled injection of interstitials in the region of the above implant via ions followed by annealing to dissolve the {311} defects; and (3) Au labeling. The reduction in Au concentration in the near-surface region (0.1–1.6 μm) with increasing interstitial injection provides the most direct evidence so far that Au labeling detects the vacancy-type defects. By correlating this reduction in Au with the known number of interstitials injected, it was determined that vacancies per trapped Au atom.

In order to elucidate the driving forces which promote oriented in-plane crystallographic texture in thin filmsdeposited on stepped substrates, a high-temperature x-ray analysis of both thin films and powders was conducted. Structuralphase transitions were found at temperatures near 350 °C and slightly above 600 °C. The transitions are tentatively indexed as orthorhombic to tetragonal and tetragonal to cubic, respectively. These results suggest that thin filmsgrow with cubic symmetry. As such, film–substrate interfacial characteristics, rather than a preferred growth direction, are believed to determine the orientation of orthorhombic twins.

Electrically active defects induced by the formation of nickel–platinum alloy monosilicide (formed at has been studied in n-type silicon using deep level transient spectroscopy and transmission electron microscopymeasurements. A Ni-related electron trap level at 0.42 eV is observed after silicidation at or above and a Pt-related electron trap level at −0.50 eV is detected after silicidation at or above. Two hole trap levels at and eV are also detected, eV level for silicidation at or above and eV level for silicidation. For the sample silicided at an additional electron trap level (located at − 0.16 eV) with a broad spectral peak is detected in the near-surface region (<0.65 μm) of the sample in which some {311} type defects of 50–100 Å long are also observed. Most of observed electrically active defects have been found to be present in near-surface regions (<2 μm). Lowest total defect concentration is observed in the sample silicided at where lowest reverse saturation current is also observed, indicating that the Ni(Pt) monosilicidation-induced electrically active defects are effective recombination/generation centers.

The effect of In surfactant during metalorganic vapor phase epitaxialgrowth on sapphire substrates on the properties of GaN layers is studied using time-resolved photoluminescence, cathodoluminescence, and scanning electron microscopy. The samples are divided into two groups, where hydrogen and nitrogen, respectively, have been used as a carrier gas during growth. It is shown that In-doped samples have a lower dislocation density, a narrower photoluminescence linewidth, and a longer free exciton lifetime. The influence of indium is stronger for GaN layers grown in nitrogen-rich conditions. The improvements of structural and optical properties are attributed to the effect of In on dislocations.

Transient properties of nonlinear refractive index change originating in photothermal effects in guest-host liquid crystal (GHLC) have been characterized by use of heat-conduction analysis. By theoretical calculations using time-dependent heat-conduction analysis, we have a time constant of about 23 ms, in good agreement with the experimental observation (about 30 ms). The characterization technique described here is very useful for characterizing the quantitative properties of photothermal effects in GHLC.

From in situ small-angle neutron scattering performed at temperatures in the undercooled liquid regime, we derive a model for the crystallization pathway of (Vit1). Vit1 first decomposes on the nanometer scale, increasing drastically the nucleation probability. In the later stages nanocrystallization occurs in one of the decomposed amorphous phases. The growth kinetics of the nanocrystals corresponds to a chemical relaxation process in which they equilibrate with the remaining amorphous matrix. Based on our model, a chemical diffusion constant is derived whose temperature dependence follows an Arrhenius law and is comparable with the expected self-diffusion constant of Ti in Vit1, as determined in independent studies of diffusion.